Bipyridine compounds are known to be useful as catalysts and organic materials, and can form complexes with various transition metals. For example, bipyridine compounds are used in a large number of chemical reactions such as a magnesium-catalyzed carbon dioxide reduction reaction, an iridium-catalyzed C—H boration reaction, and a nickel-catalyzed electrophilic cross-coupling reaction. In addition, bipyridine compounds are known to be useful as intermediates and raw materials of organic electroluminescence (organic EL) materials, pharmaceuticals, agricultural chemicals, and the like.
As a method for synthesizing a bipyridine compound, a method is reported in which 4-tert-butylpyridine-N-oxide is synthesized by reacting 4-tert-butylpyridine and peracetic acid, 4-tert-butyl-2-chloropyridine is synthesized by reacting 4-tert-butylpyridine-N-oxide with phosphoryl chloride and substituting hydrogen at 2-position with chlorine, and then 4,4′-di-tert-butyl-2,2′-bipyridine is synthesized through dimerization of 4-tert-butyl-2-chloropyridine performed in the presence of nickel bromide and a manganese catalyst (see Non-Patent Documents 1 and 2, for example).
In addition, as a method for manufacturing 2,4′-bipyridine, a technique is known in which 4-pyridylboronic acid and 2-chloropyridine are reacted using a butanol solvent in the presence of a palladium catalyst, sodium carbonate, and water, and the reaction mixture is separated into an organic layer containing 2,4′-bipyridine and an aqueous layer through liquid-liquid separation (see Example 1 in Patent Document 1, for example). A technique is disclosed in which thereafter, 2,4′-bipyridine is purified by extracting the water layer with butanol, mixing the resultant butanol layer with the previous organic layer, washing the mixed organic layer using water followed by filtration, concentrating the obtained filtrate, and distilling this concentrated solution (see Example 11). Patent Document 1 states that the purity is 98.5% and the collection yield is 47% as a result of this process.